Transmission

ABSTRACT

A transmission includes: a shift member, adapted to be moved in a shifting direction and a selecting direction; a shift lug, having a pair of claw portions spaced apart from each other in the shifting direction; and a shift fork, connected to the shift lug via a shift rail. The shift member is moved by an actuator to push one of the claw portions in the shifting direction to thereby selectively move the shift lug in the shifting direction so as to cause the shift fork to perform a gear shift operation via the shift rail. The pair of claw portions are disposed so as to be offset from each other in the selecting direction.

BACKGROUND OF THE INVENTION

The present invention relates to a mechanical transmission, and moreparticularly to the construction of a transmission unit of atransmission which includes dual clutches.

There are known mechanical automatic transmissions which use no torqueconverter, as transmissions for vehicles. In these mechanical automatictransmissions, operations (gear selection and shift) in a transmissionof a manual transmission and engagement and disengagement of clutchesare performed by an actuator, whereby automatic gear changes requiringno torque converters are enabled. The transmission includes a shiftshaft which can be moved in a shifting direction and a selectingdirection through sliding and rotating, a plurality of shift lugs (shiftbrackets) which are arranged in the selecting direction, and shift rails(rods) which connect the shift lugs and shift forks, respectively.Furthermore, a shift member (shifter), which is formed into a pawlshape, is provided on the shift shaft in such a manner as to projectoutwards, and a pair of claw portions is provided on each shift lug insuch a manner as to be spaced apart from each other in the shiftingdirection. In addition, the shift shaft is moved by the actuator in themechanical automatic transmission, whereby the claw portion of the shiftlug is selectively pushed to be moved in the shifting direction by theshift member, so that the shift fork is operated to be movedselectively.

Furthermore, in the mechanical automatic transmissions, dual clutch typeautomatic transmissions having two clutches have been developed. In thedual clutch type automatic transmissions, from a state in which one gearis engaged via one of the clutches, a target gear is engaged via theother clutch, and when the rotational speed of the target gear comes tosynchronize with that of the gear engaged via the one clutch, the oneclutch is disengaged, whereby no neutral state takes place during thegearchange, and a gearchange is enabled in which there is virtually nointerruption of power flow as the gearchange takes places.

In this way, in the dual clutch type automatic transmission, since shiftoperations for the two gears are performed sequentially during thegearchange, the movements of the shift member become complex, and as aresult, there is caused a fear that the shifting time becomes long. Tocope with this, there has been proposed a mechanical automatictransmission in which a space between a pair of claw portions providedon each shift lug is expanded in the shifting direction, so that a shiftmember can enter between the pair of claw portions on the shift lug fora target gear which is in a neutral position only by shifting the shiftmember from between the pair of claw portions of the shift lug which isin a shifted state in the selecting direction, the movements of theshift member being thereby simplified (refer to JP-A-2001-304411).

In JP-A-2001-304411, however, in order for the shift member to enterbetween the pair of claw portions when the shift member is moved to theselecting direction, the pair of claw portions must be disposed in sucha manner that the space between the pair of claw portions is expandedrelatively wide. Consequently, when a gear is engaged, since a distanceover which the shift member is moved from its neutral position to theclaw portion for abutment becomes relatively long, there is caused afear that a quick shift is not attained.

In addition, in the event that the pair of claw portions are disposed insuch a manner that the space therebetween is expanded relatively wide,force transmitted from the shift member to the claw portion becomessmall, and the efficiency is deteriorated. Hereinafter, the reason forthe deteriorated efficiency will be described using FIG. 7. FIG. 7 is aschematic diagram showing the construction of a shift mechanism of ashift lug according to the related art (JP-A-2001-304411).

As is shown in FIG. 7, in the mechanical automatic transmissiondescribed in JP-A-2001-304411, a construction is adopted in which ashift member 71 is caused to swing by rotation of a control shaft 70 soas to push a claw portion 73 of a shift lug 72 in a shifting direction.In the construction like this, when a space L1 between a pair of clawportions 73 is increased, the shift member 71 is caused to push the clawportion 73 while the shift member 71 is tilted largely towards theshifting direction. Assuming that a force exerted on the claw portion 73by a rotational torque T of the control shaft 70 then is a tangentialforce F, a distance from a contact point a between the shift member 71and the claw portion 73 to an axial center C of the control shaft 70 isa distance L2, and a tilt angle of a line which connects the contactpoint a with the axial center C towards the shifting direction is anangle a, a component of the tangential force F in the shiftingdirection, that is, a component force P1 which is a force which shiftsthe shift lug 72 in the shifting direction is obtained by the followingequation (1).

P1=F×COS α=T×COS α/L2   (1)

In the equation (1), in the event that the distance L2 is substantiallyconstant irrespective of the angle α, it is found that when the angle αis increased within a range of 0 to 90 degrees, the component force P1is decreased. Consequently, in the event that the space L1 between thepair of claw portions 73 is increased as in JP-A-2001-304411, the forcepushing the claw portion 73 towards the shifting direction is decreased,and hence, it becomes difficult to move the shift lug 72 in the shiftingdirection with good efficiency.

SUMMARY

It is therefore an object of the invention to provide a transmissionwhich enables quick and efficient gearchanges by simplifying themovements of the shift member without expanding largely the spacebetween the pair of claw portions provided on the shift lug.

In order to achieve the object, according to the invention, there isprovided a transmission, comprising:

a shift member, adapted to be moved in a shifting direction and aselecting direction;

a shift lug, having a pair of claw portions spaced apart from each otherin the shifting direction; and

a shift fork, connected to the shift lug via a shift rail, wherein

the shift member is moved by an actuator to push one of the clawportions in the shifting direction to thereby selectively move the shiftlug in the shifting direction so as to cause the shift fork to perform agear shift operation via the shift rail, and

the pair of claw portions are disposed so as to be offset from eachother in the selecting direction.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exemplary diagram of a dual clutch type automatictransmission with six forward gears and one reverse gear to which theinvention is applied.

FIG. 2 is a perspective view showing the construction of an operatingmechanism of shift forks.

FIG. 3 is a plan view showing the configuration of a shift lug.

FIG. 4 is an explanatory diagram illustrating shifting of controlfingers in changing gears according to an embodiment of the invention.

FIG. 5 is an explanatory diagram illustrating shifting of controlfingers in changing gears according to a related art transmission.

FIG. 6 is a schematic diagram showing the construction of a shiftingmechanism of the shift lug according to the embodiment.

FIG. 7 is a schematic diagram showing the construction of a shiftingmechanism of the shift lug according to the related art transmission.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, an embodiment of the invention will be described based onthe accompanying drawings.

FIG. 1 is an exemplary diagram of a transmission unit 1 of a dual clutchtype transmission with six forward gears and one reverse gear to whichthe invention is applied.

As is shown in FIG. 1, the transmission unit 1 includes two clutches 2,3, two main shafts 4, 5 which are disposed concentrically and twocounter shafts 6, 7. Power is configured to be delivered to the firstmain shaft 4 from an output shaft 9 of an engine 8 via the first clutch2, while the power is configured to be delivered to the second mainshaft 5 from the output shaft 9 via the second clutch 3.

The first counter shaft 6 and the second counter shaft 7 are disposedspaced apart in such a manner that their axes become parallel to thoseof the first main shaft 4 and the second main shaft 5 and are configuredto be able to deliver the power to a differential 10 which is disposedat a final stage of the transmission unit 1. A first speed gear 11, asecond speed gear 12, a third speed gear 13 and a sixth speed gear 14are pivotally supported on the first counter shaft 6 in such a manner asto rotate thereon. A fourth speed gear 15, a fifth speed gear 16 and areverse gear 17 are pivotally supported on the second counter shaft 7 insuch a manner as to rotate thereon, and a parking gear 18 is fixed tothe second counter shaft 7.

In addition, four shift forks 20 to 23 are provided in the transmissionunit 1. A first shift fork 20 and a second shift fork 21 are placed insuch a manner as to slide to be moved along the axis of the firstcounter shaft 6, and a third shift fork 22 and a fourth shift fork 23are placed in such a manner as to slide to be moved along the axis ofthe second counter shaft 7. By sliding to move these shift forks 20 to23, the second speed gear 12 and the sixth speed gear 14 are allowed toselectively come in or out of engagement with the first counter shaft 6(gearchange operations) by the first shift fork 20, and the first speedgear 11 and the third speed gear 13 are allowed to selectively come inor out of engagement with the first counter shaft 6 (gearchangeoperations) by the second shift fork 21. In addition, the fourth speedgear 15 and the reverse gear 17 are allowed to selectively come in orout of engagement with the second counter shaft 7 (gearchangeoperations) by the third shift fork 22, and the fifth speed gear 16 andthe parking gear 18 are allowed to selectively come in or out ofengagement with the second counter shaft 7 (gearchange operations) bythe fourth shift fork 23. The first speed gear 11, the third speed gear13 and the fifth speed gear 16 are connected to the first main shaft 4,while the second speed gear 12, the fourth speed gear 15, the sixthspeed gear 14 and the reverse gear 17 are connected to the second mainshaft 5.

Namely, in the transmission unit 1 of the dual clutch type transmission,gearchanges to/from the first speed gear, the third speed gear and thefifth speed gear can selectively be attained by way of the first clutch2, while gearchanges to/from the second speed gear, the fourth speedgear, the sixth speed gear and the reverse gear can selectively beattained by way of the second clutch 3.

FIG. 2 is a perspective view showing the construction of an operatingmechanism of the shift forks 20 to 23.

As is shown in FIG. 2, the shift forks 20 to 23 are fixed, respectively,to four shift rails 30 which are disposed in such a manner as to move ina back and forth direction (a shifting direction), and furthermore,shift lugs 40 are provided on the shift rails 30, respectively. Theshift lug 40 is a sheet material which is formed into a U-shape to openupwards and is disposed in such a manner that claw portions 41 providedat an upper end portion thereof align in the back and forth direction.The shift lugs 40 are disposed in such a manner that center lines oftheir openings in the back and forth direction align with one another insuch a state that they are disengaged (or in neutral positions).

A shift shaft 50 is supported above the shift lugs 40 in such a manneras to extend over the center lines of the openings in the back and forthdirection so as to be rotated and moved in an axial direction (aselecting direction). Pawl-like control fingers 51 (shift members) areformed on the shift shaft 50 in such a manner as to project downwardstherefrom. Two control fingers 51 are provided in such a manner as to bespaced apart from each other in the axial direction, and the controlfingers 51 are disposed in such a way that one control finger 51 isinserted into the openings of the two shift lugs 40.

When the shift shaft 50 is slid in the axial direction so that thecontrol finger 51 is positioned in the opening of the shift lug 40 for atarget gear and the shift shaft 50 is then rotated to push the clawportion 41 of the shift lug 40 with the control finger 51, the shiftforks 20 to 23 can be moved in the back and forth direction via theshift rails 30, so that the gears corresponding to the shift forks 20 to23 can be engaged or disengaged for gearchange operations.

The shift shaft 50 is driven to rotate by a shifting motor 60 and isdriven to slide in the axial direction by a selecting motor 61 via aball screw 63. The shifting motor 60 and the selecting motor 61 arecontrolled to be driven by an ECU 62 based on the operation of agearshift lever, not shown, and the running conditions of the engine 8and are controlled to be driven in such a manner that gearchanges takeplace sequentially, for example, when a gearchange to a target gear isimplemented. The ECU 62 also controls the operations of the clutches 2,3 when gearchanges take place. Specifically, in changing gears, the ECU62 controls the other clutch 3 or 2 to be engaged to engage the nextgear from a state resulting before a gearchange has taken place in whichone of the clutches 2 or 3 is engaged while maintaining the engagementof a gear which is engaged by the one of the clutches 2 or 3. Then, at apoint in time at which the rotational speed of the gear that has justbeen engaged comes to synchronize with that of the previous gear, thelatter gear is disengaged so as to realize a gearchange in which thereis virtually no interruption of power flow as the gearchange takesplace.

FIG. 3 is a plan view showing the configuration of the shift lug 40.

As is shown in FIG. 3, the shift lug 40 of this embodiment is formedtwisted in such a manner that the pair of confronting claw portions 41are disposed to be offset from each other in the axial direction. Thatis, the confronting claw portions 41 are displaced with each other inthe axial direction (the selecting direction).

FIG. 4 is an explanatory diagram which illustrates shifting of thecontrol fingers 51 when a gearchange takes place. In this figure, as anexample, shifting steps of the control fingers 51 are shown from thecompletion of a gearchange to the fourth speed gear by disengaging theprevious or third speed gear to the completion of a gearchange to thefifth speed gear.

In the figure, a vertical direction denotes the shifting direction and ahorizontal direction denotes the selecting direction. A verticallycentral position denotes a neutral position. Each pair of claw portions41 is made to be moved one scale vertically in the figure, and by beingmoved vertically outwards, a gearchange is made to the gear whichcorresponds to the claw portion so moved. In addition, the controlfingers 51 are made to be moved one scale vertically from the verticalcenter in the figure when the shift shaft 50 is rotated.

(Stand-by state) This stand-by state is a state in which a gearchange tothe fourth speed gear has just been completed. In the stand-by state,the right-hand control finger 51 a has pushed an inner side of thefourth speed gear claw portion 41 f so as to move it outwards, wherebythe fourth speed gear is engaged. In this state, the third speed gearclaw portion 41 c is also moved outwards.

-   (Step 1) The control fingers 51 a, 51 b are moved to upper shift    positions as viewed in the figure.-   (Step 2) The control fingers 51 a, 51 b are moved leftwards in the    figure, so that the left-hand control finger 51 b is moved to the    same horizontal position (the same position in the selecting    direction) as the first speed gear claw portion 41 d.-   (Step 3) The control fingers 51 a, 51 b are moved downwards to the    neutral position in the figure, whereby the left-hand control finger    51 b pushes an inner side of the first speed gear claw portion 41 d    so as to move it downwards. Consequently, the third speed gear claw    portion 41 c is moved to the neutral position, whereby the third    speed gear is disengaged (completion of disengagement of the    previous).-   (Step 4) The control fingers 51 a, 51 b are moved rightwards in the    figure, so that the right-hand control finger 51 a is brought into    abutment with a left side of the reverse claw portion 41 e.-   (Step 5) The control fingers 51 a, 51 b are moved downwards in the    figure, so that the right-hand control finger 51 a is brought into    abutment with an inner side of the fourth speed gear claw portion 41    f.-   (Step 6) The control fingers 51 a, 51 b are moved rightwards in the    figure, so that the right-hand control finger 51 a is brought into    abutment with a left side of the parking gear claw portion 41 h.-   (Step 7) The control fingers 51 a, 51 b are moved upwards in the    figure, so that the right-hand control finger 51 a pushes an inner    side of the fifth speed gear claw portion 41 g so as to move the    fifth speed gear claw portion 41 g to a shift position, whereby a    gearchange to the fifth speed gear is completed.

Thus, in the embodiment, the gearchange from the completion ofengagement of the fourth speed gear to the completion of engagement ofthe fifth speed gear is completed through seven steps.

Next, shifting steps of control fingers 51 in a transmission unitaccording to the related art will be described as a comparison example.

FIG. 5 is an explanatory diagram which illustrates shifting of thecontrol fingers 51 when a gearchange takes place, and shifting steps ofthe control fingers 51 are shown from the completion of a gearchange tothe fourth speed gear by disengaging the previous or third speed gear tothe completion of a gearchange to the fifth speed gear.

In the transmission unit of the related art, a pair of claw portions 41of each shift lug 40 is not offset in the shifting direction but isdisposed in the same position in the shifting direction.

(Stand-by state) As with the embodiment of the invention, the right-handcontrol finger 51 a has pushed an inner side of the fourth speed gearclaw portion 41 f′ so as to move it outwards, whereby the fourth speedgear is engaged. In this state, the third speed gear claw portion 41 c′is also moved outwards.

-   (Step 1) The control fingers 51 a, 51 b are moved leftwards in the    figure, so that the left-hand control finger 51 b is brought into    abutment with a right side of the first speed gear claw portion 41    d′.-   (Step 2) The control fingers 51 a, 51 b are moved to upper shift    positions in the figure.-   (Step 3) The control fingers 51 a, 51 b are moved leftwards in the    figure, so that the left-hand control finger 51 b is moved to the    same horizontal position as the first speed gear claw portion 41 d′.-   (Step 4) The control fingers 51 a, 51 b are moved downwards to the    neutral position in the figure, whereby the left-hand control finger    51 b pushes an inner side of the first speed gear claw portion 41 d′    so as to move it downwards. Consequently, the third speed gear claw    portion 41 c′ is moved to the neutral position, whereby the third    speed gear is disengaged (completion of disengagement of the    previous gear).-   (Step 5) The control fingers 51 a, 51 b are moved rightwards in the    figure, so that the right-hand control finger 51 a is brought into    abutment with a left side of the reverse gear claw portion 41 e′.-   (Step 6) The control fingers 51 a, 51 b are moved downwards in the    figure so as to be moved to lower shift positions in the figure.-   (Step 7) The control fingers 51 a, 51 b are moved rightwards in the    figure, so that the right-hand control finger 51 a is brought into    abutment with a left side of the parking gear claw portion 41 h′.-   (Step 8) The control fingers 51 a, 51 b are moved upwards to the    neutral position in the figure.-   (Step 9) The control fingers 51 a, 51 b are moved rightwards in the    figure, so that the right-hand control finger 51 a is moved to the    same horizontal position as the fifth speed gear claw portion 41 g′.-   (Step 10) The control fingers 51 a, 51 b are moved upwards in the    figure, so that the right-hand control finger 51 a pushes an inner    side of the fifth speed gear claw portion 41 g′ so as to move the    fifth speed gear claw portion 41 g′ to the shift position, whereby    the gearchange to the fifth speed gear is completed.

As has been described heretofore, in the transmission unit of therelated art, ten steps are required from the completion of gearchange tothe fourth speed gear to the completion of gearchange to the fifth speedgear.

In the embodiment of the invention, since the pair of claw portions 41of each shift lug 40 is formed in such a manner as to be offset in theshifting direction, when shifting the control finger 51 which ispositioned between the pair of claw portions 41 of the shift lug 40towards the neutral position while maintaining the engagement of thegear, two steps (from the stand-by state to step 2) are required,whereas in the embodiment, the shifting is completed in one step (fromthe stand-by state to step 1). In addition, when shifting the controlfinger 51 which is in abutment with a side of one of the claw portions41 of the shift lug 40 which is in the neutral position to the otherclaw portion 41 so as to push it outwards to thereby shift the shift lug40, three steps (from step 7 to step 10) are required in the related arttransmission unit, whereas in the embodiment, the shifting is completedin one step (from step 6 to step 7).

In this way, in the embodiment, since the number of shifting steps ofthe control fingers 51 can be reduced largely when a gearchange takesplace, a reduction in shift time can be realized. In addition, also inchanging gears to the other speed gears, the number of shifting steps ofthe control fingers 51 can be reduced.

In the embodiment, since the necessity is obviated of expanding largelythe space between the pair of claw portions of the shift lug 40 relativeto the control finger 51 as has taken place in the related arttransmission unit, once it is moved, the control finger 51 can bebrought into abutment with the claw portion 41 immediately, therebymaking it possible to enable a quick gearchange.

FIG. 6 is a schematic diagram showing the construction of the shiftingmechanism of the shift lug according to the embodiment.

In this embodiment, since the space L3 between the pair of claw portions41 can be set relatively narrow, the control finger 51 is allowed topush the claw portion 41 while it is tilted little in the shiftingdirection. Assuming that a force exerted on the claw portion 41 by arotational torque T of the shift shaft 50 then is a tangential force F,a distance from a contact point a between the control finger 51 and theclaw portion 41 to an axial center C of the shift shaft 50 is a distanceL4, and a tilt angle of a line which connects the contact point a withthe axial center C of the shift shaft 50 towards the shifting directionis an angle β, a component of the tangential force F in the shiftingdirection, that is, a component force P2 which is a force which shiftsthe claw portion 41 in the shifting direction is obtained by thefollowing equation (2).

P2=F×COS β=T×COS β/L4   (2)

Consequently, in this embodiment, since the space L3 between the pair ofclaw portions 41 is relatively narrow and hence the angle β issuppressed to a smaller angle, as is expressed by the equation (2), thecomponent force 2 is reduced largely relative to the tangential force Fin no case. In addition, since the distance L4 remains substantiallyconstant irrespective of the angle β, the rotational torque T of theshift shaft 50 is transmitted with good efficiency as a force whichpushes the claw portion 41 in the shifting direction, thereby making itpossible to move the shift lug 40 in the shifting direction with goodefficiency.

In addition, since the control fingers 51 are provided more than one,even in the event that there are many gears to be changed, each controlfinger 51 is made to operate some of the shift lugs for gearchanges,whereby the shifting distance of each control finger in the shiftingdirection can be suppressed to a shorter distance. Consequently, theshifting mechanism of the control fingers 51 can be made compact in sizewith respect to the shifting direction.

In addition, the direction in which the claw portions 41 are offset maybe set appropriately on each of the shift lugs depending upon the numberand arrangement of gears. Additionally, the invention can be applied toa transmission unit with a different number of gears from theembodiment, and the number of control fingers 51 may be setappropriately depending upon the number of gears to be provided.

According to an aspect of the invention, by setting appropriately theoffset direction of the claw portions in accordance with the arrangementof the shift rail, when the shift member is moved in the slidingdirection so as to be brought into abutment with a side of one of theclaw portions to change gears, in the event that, following this, theshift member is moved in the shifting direction, the shift member can bebrought into abutment with an inner side of the other claw portion.Consequently, since the movements of the shift member in changing gearsare simplified without expanding largely the space of the pair of clawportions, a quick and efficient gearchange can be attained.

According to an aspect of the invention, the shift member can be movedin the shifting direction and the selecting direction by rotating andshifting the shaft in the selecting direction by the actuator.Consequently, the shifting mechanism for shifting the shift member inthe shifting direction and the selecting direction can be realized withthe simple configuration.

According to an aspect of the invention, since the shift member isprovided more than one on the shaft in such a manner as to be spacedapart from each other in the selecting direction, even in the event thatthere are many gears to be changed and hence so many shift rails arerequired, each shift member can be set to operate some of the shiftrails for gearchanges, whereby the shifting of each shift member in theselecting direction can be reduced. Consequently, the shifting mechanismof the shift members can he made compact in size with respect to theselecting direction.

1. A transmission, comprising: a shift member, adapted to be moved in ashifting direction and a selecting direction; a shift lug, having a pairof claw portions spaced apart from each other in the shifting direction;and a shift fork, connected to the shift lug via a shift rail, whereinthe shift member is moved by an actuator to push one of the clawportions in the shifting direction to thereby selectively move the shiftlug in the shifting direction so as to cause the shift fork to perform agear shift operation via the shift rail, and the pair of claw portionsare disposed so as to be offset from each other in the selectingdirection.
 2. The transmission as set forth in claim 1, wherein aplurality of the shift lug are arranged in the selecting direction, anda plurality of the shift folk are connected to the plurality of theshift lug, respectively.
 3. The transmission as set forth in claim 1,further comprising: a shaft, extended in the selecting direction, andadapted to be moved in the selecting direction and rotated, by theactuator, wherein the shift member projects from an outer circumferenceof the shaft.
 4. The transmission as set forth in claim 3, wherein aplurality of the shift member are provided on the shaft and are spacedapart from each other in the selecting direction.